Dissertation Defence: Development of High and Low Fidelity Models for Wind Farm-Atmospheric Boundary Layer Interaction

Sebastiano Stipa, supervised by Dr. Joshua Brinkerhoff, will defend their dissertation titled “Development of High and Low Fidelity Models for Wind Farm-Atmospheric Boundary Layer Interaction” in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Mechanical Engineering.

An abstract for Sebastiano Stipa’s dissertation is included below.

Examinations are open to all members of the campus community as well as the general public.

Registration is not required for in person exams.

---

ABSTRACT

In the past decade, the increase in the number and scale of wind energy projects has exposed deficiencies in the approach adopted by industry to assess potential wind farm sites. While current analytical models are sufficiently accurate for isolated rotors or small wind parks, they fall short in accurately representing the flow physics around large turbine arrays. This discrepancy arises from neglecting the mutual wind farm interaction with the thermally-stratified atmospheric boundary layer (ABL), which leads to the following two main effects. Firstly, the increased shear stress within the wind farm augments momentum vertical fluxes, affecting the wind speed at the turbine locations and in the cluster wake. Secondly, the wind farm displaces the boundary layer vertically, triggering atmospheric gravity waves that induce horizontal pressure gradients which alter the velocity field within the ABL, ultimately affecting wind farm power production. These dynamics may imply an extended blockage region upstream of the farm and a favorable pressure gradient inside.

To comprehend these physical aspects, the highly-parallel, open-source, finite volume, large eddy simulation (LES) code TOSCA (Toolbox fOr Stratified Convective Atmospheres) has been developed. TOSCA enables simulation of the flow around a finite-size wind farm immersed in a thermally stratified ABL, evaluating gravity wave-induced blockage effects and the formation of large wind farm cluster wakes. Additionally, three engineering parametrizations have been developed to capture wind farm blockage and cluster wakes. The first, the multi-scale coupled (MSC) model, utilizes a novel micro-to-mesoscale coupling approach, predicting small scale effects at the wind turbine scale and meso-scale phenomena at the wind farm scale. The MSC model has been then coupled with a novel wind farm wake model that allows to capture the long wakes produced by large wind farm clusters. Lastly, a model predicting the evolution of the shear stress profile within and downstream of a wind farm cluster has been developed. These reduced-order parametrizations have undergone successful verification against TOSCA LES results, demonstrating their enhanced accuracy in capturing the targeted physical processes compared to current industry-standard engineering models.